Hard-disk drives provide data storage for data processing systems in computers and servers, and are becoming increasingly pervasive in media players, digital recorders, and other personal devices. Recent advances in hard-disk drive technology allow more digital information to be stored on increasingly smaller disks. Recent developments also have simplified hard-disk drive manufacturing processes while yielding increased track densities, thus promoting increased data storage capabilities at reduced costs.
Generally, to write data to a hard disk drive, a read/write head can initiate an electromagnetic field that orients a cluster of magnetic grains, known as a bit, in one direction or the other. To increase the capacity of disk drives, manufacturers have been striving to reduce the size of bits and the grains that make up the bits. Recently, patterned media have been developed in which a magnetic thin film layer is created as an ordered array of highly uniform islands each capable of storing an individual bit. This structure enlarges the disk capacity by imposing sharp magnetic transitions at well-defined pre-patterned positions or bit patterns that are organized as concentric data tracks around a disk.
Because of the tightly-spaced bits, a head-positioning servo mechanism can be used to facilitate the ability of the read/write head to locate a particular data track location and to reposition the read/write head from one location to another. Indexing marks and alignment indices may be recorded in arc-shaped regions on the data tracks, known as servo sectors, and referenced by the servo mechanism to maintain proper dynamic positioning capabilities of the read/write head over time. Track addresses, synchronization signals, and position error signal (“PES”) bursts may also be recorded in the servo sectors.